The U.S. Border Patrol is running daily citizenship checks on buses traveling from Fort Kent toward the state's interior and making periodic checks on buses originating in Bangor. Civil rights advocates say these checks may be in violation of protections outlined in the U.S. Constitution.

Daniel Heibert, chief patrol agent for the Houlton sector, says the agency has the authority to make such checks anywhere within 100 miles of the border, a standard which encompasses the entire state of Maine.

"Our purpose for boarding any conveyances, a bus specifically in this case, would be to question anybody – anybody – about their right to be or remain in the United States, whether they are an alien or not,” says Heibert. “That's kind of the gist of it. We would have to have a reasonable suspicion to think that somebody isn't a citizen to continue questioning."

The daily checks, he says, might occur at any number of stops routinely made on the Cyr Bus Line's routes. He also says a boarding on a Concord Trailways bus at the Bangor bus depot last December did find an individual who was, "out of status," that is, not legally in the country. The checks that take place away from the immediate border, he says, provide a useful means of testing the patrol's efforts to police the border itself.

"It's an effective use of the limited resources that we have and kind of validate what you're doing based on what you're catching there,” Heibert says. “You get information from the passengers on people. They might be getting on or off the bus ahead of or after the transportation checks."

Zach Heiden of The ACLU of Maine is questioning the checks.

"We don't want to live in a 'show-me-your-papers' kind of society," says Heiden .

Heiden says these checks may violate civil rights to freedom of movement or against unreasonable search and seizure.

"The Bill of Rights and the Constitution protect us everywhere in this country,” Heiden says, “but sometimes customs and the border patrol like to pretend that there's a constitution-free zone anywhere within a hundred miles of the border."

Heiden says the border patrol's activities in Maine raise the possibility of racial profiling. Chief Agent Hiebert, though, says agents can ask questions based on nationality, questions that are not based on race or skin color. Hiebert adds that agents are trained to perform their tasks in a way that does not inhibit freedom of movement.

Agent Hiebert says that while U.S. citizens are not required to carry ID, others are required to carry documentation of their status.

Hiebert declined to provide more information on the recent Bangor detainee, citing the formal process set in motion by a Freedom of Information Act request from the ACLU.

The general manager for Cyr Bus Line, Rick Soules, says he doesn't often hear from customers or drivers about the patrol checks, but when he does, it's positive.

"The feelings I get generally from people regarding the border checks are that it's a safety check, which provides security for the people riding the bus, and that they're not put out by that," says Soules.

Concord Coach Lines officials could not immediately be reached for comment.

Last week, a video that went viral showed border patrol agents in Florida boarding a Greyhound bus, and asking passengers for ID and removing a woman who they said had overstayed her tourist visa. This incident sparked outrage online and from advocacy groups.

Agent Hiebert says transportation checks in Maine were discouraged under President Obama, but have become more frequent since President Trump took office.